Furnace Blower Fan on 100% of the time - Good or Bad or it depends?

I was at a dinner party last night and two guests described how their HVAC reps told them to run their furnace blowers 100% of the time. The HVAC reps reasons for the recommendation, as relayed by the dinner guests, were:

1. continuous running reduces the wear and tear on the blower motor that cycling on and off causes, thereby avoiding an earlier motor replacement

2. circulating the air around the home provides better balanced temperatures throughout the home and,

3. continuous air flow would provide cleaner air due to the continuous filtering.

We live in northern Michigan and are a heating dominate climate. I am curious to hear from the HVAC professionals about what they recommend to their clients and why. At the moment I don't buy the above arguments and feel those customers end up paying more in energy costs for little benefit. However I do understand there is no disputing tastes when talking about perceived comfort. Also if anyone knows of a good source or any research done on this issue I would like to see a more in depth analysis (if its out there).

[NOTE: Neither home has an ERV, HRV, or other mechanical ventilation other than intermittent bath and kitchen fans. Both are natural gas, forced air furnaces.]

Good question. My home is 20 years old and so far it looks like the discussion regarding electricity costs being higher but what about the overall cost of energy. The last two days I did a test one with the fan set to auto and the next with the fan set to on. The first day the high was 19 and the low was 8 degrees. The heat was on for 14 hours. The next day at 6:00 AM (when I had the idea), I switched the fan to on. The hight for that day was 19 with a low of 7 degrees which is fairly consistent with the previous day. For that day, the heat was on for only 8 hours. So while I was using more electricity running the fan, the natural gas usage was cut dramatically. I don't know if that is typical or how this impacts the overall energy costs between the two scenarios.

Good question. My home is 20 years old and so far it looks like the discussion regarding electricity costs being higher but what about the overall cost of energy. The last two days I did a test one with the fan set to auto and the next with the fan set to on. The first day the high was 19 and the low was 8 degrees. The heat was on for 14 hours. The next day at 6:00 AM (when I had the idea), I switched the fan to on. The hight for that day was 19 with a low of 7 degrees which is fairly consistent with the previous day. For that day, the heat was on for only 8 hours. So while I was using more electricity running the fan, the natural gas usage was cut dramatically. I don't know if that is typical or how this impacts the overall energy costs between the two scenarios.

David,
I am here in the Chicago area and had pretty much the same temp as you. Question #1 You say the heat was on all day, does that mean that you counted how many times it shut down and started back up? This was in your auto position. Question #2 when you switched to fan, are you saying the furnace did not run as often, did you count how many times it went off and on?
When I put mine in auto, it seemed to have run all day, maybe off for a few minutes then back on. When I put the fan on, I did not notice any change, it ran all day, but not sure how often.

So, I tend to agree with you...if you keep the fan on all the time, wouldn't it make sense that when the furnace called for heat, and since the blower is already running, wouldn't it take less energy to get that blower motor to get to it's first stage.

And yep, if you saved on that....did you electricity bill just go up? :)

We live in the same Chicagoland area. Regarding question #1, it would seem that about a minute later the system would kick back on in the auto mode. For the usage on both days, all I'm going off of is the usage stats on the thermostat. Since I'm only day two with the fan running continuously, I don't know where the energy bills will end up. As the temp warms up to around 30, I may switch it back to auto. I'm not sure how many Therms I"m using during both of these days. Knowing that would be useful to extrapolate any costs increases/decreases.

Bruce Gold said:

David Mileusnich said:

Good question. My home is 20 years old and so far it looks like the discussion regarding electricity costs being higher but what about the overall cost of energy. The last two days I did a test one with the fan set to auto and the next with the fan set to on. The first day the high was 19 and the low was 8 degrees. The heat was on for 14 hours. The next day at 6:00 AM (when I had the idea), I switched the fan to on. The hight for that day was 19 with a low of 7 degrees which is fairly consistent with the previous day. For that day, the heat was on for only 8 hours. So while I was using more electricity running the fan, the natural gas usage was cut dramatically. I don't know if that is typical or how this impacts the overall energy costs between the two scenarios.

David,I am here in the Chicago area and had pretty much the same temp as you. Question #1 You say the heat was on all day, does that mean that you counted how many times it shut down and started back up? This was in your auto position. Question #2 when you switched to fan, are you saying the furnace did not run as often, did you count how many times it went off and on?When I put mine in auto, it seemed to have run all day, maybe off for a few minutes then back on. When I put the fan on, I did not notice any change, it ran all day, but not sure how often.

So, I tend to agree with you...if you keep the fan on all the time, wouldn't it make sense that when the furnace called for heat, and since the blower is already running, wouldn't it take less energy to get that blower motor to get to it's first stage.

And yep, if you saved on that....did you electricity bill just go up? :)

We live in the same Chicagoland area. Regarding question #1, it would seem that about a minute later the system would kick back on in the auto mode. For the usage on both days, all I'm going off of is the usage stats on the thermostat. Since I'm only day two with the fan running continuously, I don't know where the energy bills will end up. As the temp warms up to around 30, I may switch it back to auto. I'm not sure how many Therms I"m using during both of these days. Knowing that would be useful to extrapolate any costs increases/decreases.

Bruce Gold said:

David Mileusnich said:

Good question. My home is 20 years old and so far it looks like the discussion regarding electricity costs being higher but what about the overall cost of energy. The last two days I did a test one with the fan set to auto and the next with the fan set to on. The first day the high was 19 and the low was 8 degrees. The heat was on for 14 hours. The next day at 6:00 AM (when I had the idea), I switched the fan to on. The hight for that day was 19 with a low of 7 degrees which is fairly consistent with the previous day. For that day, the heat was on for only 8 hours. So while I was using more electricity running the fan, the natural gas usage was cut dramatically. I don't know if that is typical or how this impacts the overall energy costs between the two scenarios.

David,I am here in the Chicago area and had pretty much the same temp as you. Question #1 You say the heat was on all day, does that mean that you counted how many times it shut down and started back up? This was in your auto position. Question #2 when you switched to fan, are you saying the furnace did not run as often, did you count how many times it went off and on?When I put mine in auto, it seemed to have run all day, maybe off for a few minutes then back on. When I put the fan on, I did not notice any change, it ran all day, but not sure how often.

So, I tend to agree with you...if you keep the fan on all the time, wouldn't it make sense that when the furnace called for heat, and since the blower is already running, wouldn't it take less energy to get that blower motor to get to it's first stage.

And yep, if you saved on that....did you electricity bill just go up? :)

Thanks for your input, much appreciated

Well David, I sure hope your onto something. I'm sure it will take a couple or few months to know about the costs...so good luck and hopefully you can keep my informed.
Thanks

David, you can check your gas consumption at the meter. If you had measured that for the two days of your experiment, I'll bet the numbers would show a very different result than your 14 hours vs. 8 hours of furnace run time that you read off the thermostat.

I have a lot of difficulty believing that keeping the fan switch set to on will cut your heating almost in half. The only way this could happen is if you had (1) a very tight house, (2) ducts inside the envelope, (3) poor distribution of heated air in the house, and (4) a thermostat in the coldest part of the house.

In houses, you lose heat through the building envelope. Keeping your fan on doesn't decrease the amount of heat loss you have there, which means you still have to keep adding as much heat as you're losing. For the reasons below, what's more likely to happen is that you increase your heat loss and have to add more heat, not less.

Keeping the fan on is likely to increase infiltration because of unbalanced duct leakage. That means you lose heat even more quickly.

Keeping the fan on is likely to send more of your heated air outside and bring in more cold air because of duct leakage. Even if you have the same amount of leakage in the supply ducts as in the returns, you're throwing out heat and bringing in cold air through those leaks. The only way to avoid this is to have NO duct leakage outside the envelope, which is only possible if all the ducts are inside the envelope.

Keeping the fan on is going to cool off your indoor air if your ducts are outside the envelope. When you run 70° air through a duct with R-4, R-6, or R-8 insulation in a space that's 20°, 40°, or more cooler, that air inside the ducts will lose heat by conduction to the surroundings.

If you go back and read some of the earlier comments (Michael Blasnik's, mine, and A. Tamasin Sterner's on the first page), you'll see that there are other good reasons not to keep the fan in the on position, too.

If you have data that you think prove that your house is an exception to the principles of building science, I'd like to see them. If your data show that you save money by keeping the fan in the on position, I'm sure an experienced building science pro could find out what the real problem is and how you can save even more money by fixing it.

David, you can check your gas consumption at the meter. If you had measured that for the two days of your experiment, I'll bet the numbers would show a very different result than your 14 hours vs. 8 hours of furnace run time that you read off the thermostat.
I have to go with this one, since when I had my fan on auto, the furnace would run as much as when the fan was in auto.
The only thing I felt was the house cooling off faster in run, then it did in auto. I think my next experiment is to have the ceiling fan blowing down in slow, since heat rises ( actually, heat does not rise but get pushed up from cold air) maybe that might make a difference.
Any comments?

I have a lot of difficulty believing that keeping the fan switch set to on will cut your heating almost in half. The only way this could happen is if you had (1) a very tight house, (2) ducts inside the envelope, (3) poor distribution of heated air in the house, and (4) a thermostat in the coldest part of the house.

In houses, you lose heat through the building envelope. Keeping your fan on doesn't decrease the amount of heat loss you have there, which means you still have to keep adding as much heat as you're losing. For the reasons below, what's more likely to happen is that you increase your heat loss and have to add more heat, not less.

Keeping the fan on is likely to increase infiltration because of unbalanced duct leakage. That means you lose heat even more quickly.

Keeping the fan on is likely to send more of your heated air outside and bring in more cold air because of duct leakage. Even if you have the same amount of leakage in the supply ducts as in the returns, you're throwing out heat and bringing in cold air through those leaks. The only way to avoid this is to have NO duct leakage outside the envelope, which is only possible if all the ducts are inside the envelope.

Keeping the fan on is going to cool off your indoor air if your ducts are outside the envelope. When you run 70° air through a duct with R-4, R-6, or R-8 insulation in a space that's 20°, 40°, or more cooler, that air inside the ducts will lose heat by conduction to the surroundings.

If you go back and read some of the earlier comments (Michael Blasnik's, mine, and A. Tamasin Sterner's on the first page), you'll see that there are other good reasons not to keep the fan in the on position, too.

If you have data that you think prove that your house is an exception to the principles of building science, I'd like to see them. If your data show that you save money by keeping the fan in the on position, I'm sure an experienced building science pro could find out what the real problem is and how you can save even more money by fixing it.

Just received my gas bill. This is just additional information and I don't have exact day for day analysis but on the days that were very cold I just left the fan on. Otherwise, I switched it back to auto. For 11/16/-12/16, the number of therms was 184 which is higher than last year but last year was much warmer. The average temp for this period just finished was 22 degress. Last December's average was 29 but January's was 23. January's therms were ~250. So it looks like a potential difference of around 60 therms if I go by average recorded temperature. I haven't received my electric bill yet.

When you reply, please put your comments somewhere other than inside the quote of the comment to which you're replying. It makes it difficult to find your replies when you put it there. Also, you don't have to keep all -- or any -- of the quoted comment. The first thing I did when I started this comment was to delete all of the quoted comment. If I want to reply point-by-point, I might keep some or all of the quoted text but make sure not to write in that part.

Trane will get back to you. They are more responsive than most companies but it will have to go to several people first. They may send it to the local distributer to handle so be patient if you can.

If the furnace is 4 yrs old the parts should be covered under warranty (5 yr ) The complete motor is VERY EXPENSIVE but you probably wont need the entire assembly. The main parts can be replaced without replacing the entire motor. Bearings can be replaced easily as well as the control module located on the back of the motor, armature and I see no reason why you would ever need to replace the magnets.

The labor will not be warrantied unless you have an extended warranty purchased at the time of sale.

Gas smells are not normal unless you eat beans

I have your address in IL if you didnt falsify your profile. Click on the name of the person replying and then click on their pic and it will take you to their profile on this site. So I know the general area you are in

Hopefully they Trane will respond quickly since it was installed, looks like 3/06. Didn't falsify anything, that way I get to keep my gun permit. :) Threw a bucket of water down the drain by the furnace...gas smell seems to have gotten better, so not sure if it was really gas or just stale water sitting in the trap that was causing the gas fumes. I am going to have my neighbors come over again tonight to see if they can still smell....THE SMELL!!!! I can, but not as much, but furnace has been running all day. I believe this is day number 6 with problem. Saturday my girlfriend told me to get some parakeets (like they did for mines), I told her that's why I invited her over for dinner...my arm is still sore. So first move is to wait for Trane...if you have any pull or strings with them, the sooner the better. So now, I go and click on your name then picture...here goes. Again,Thanks. And I am assuming you are an HVAC tech. I will have at least one last question for you probably tomorrow.

Steven, Hope your still there, since I have a new question.

What problems would my furnace have if it is pitched back. Meaning, from the top, the furnace goes back slightly until it get to the bottom, then it is at least 1/2 off...meaning back from the top.

Had a new blower motor installed, now they are coming out today to install a inducer motor for the 3 time.

Now just getting the run around from this company about when they will fix this pitch problem. This is going on almost 5 years and believe now, they will not come out to fix this until they get all their installs done leaving me with new parts and yet a badly pitched furnace.